The experiments encompassed in this proposal will examine the basic cytological organization of the vaginal epithelium of the rhesus monkey during the menstrual cycle and during pregnancy. Thin-sections and freeze-fracture electron microscopy will be used to analyze cell organelle and cell membrane changes during cell differentiation in the basal, intermediate, and superficial layers of this keratinizing epithelium. In addition, the nature of the intercellular junctions in the different layers of the epithelium will be studied. The permeability of the vaginal epithelium will be studied using electron-dense tracer molecules such as lanthanum, peroxidase, and ferritin. Changes in epithelial permeability in relation to the structure of the epithelium at different stages of the cycle will be studied. The cytological basis of attachement of indigenous bacterial to the superficial epithelial cells will be studied by thin-section, freeze-fracture and scanning electron microscopy. Enzymatic digestions and various chemical manipulations as well as the addition of carbohydrates and lectins will be used as initial probes of the biochemical basis of bacterial cell-epithelial cell attachment.